Rought example of an xhr POST request with a file

xhr-POST-with-file.js

 var str_title   = document.querySelector('#category_box_title').value;
 var str_url     = document.querySelector('#category_box_url').value;
 var arr_image   = document.querySelector('#category_box_image').files[0];
 var int_id      = document.querySelector('#category_box_id').value;
 var formData = new FormData();
 formData.append('title', str_title);
 formData.append('url', str_url);
 formData.append('image', arr_image);
 formData.append('web_page_content_widget_id', int_selected_content_widget_id);

 if (int_id.length > 0) {
    var str_action = 'update';
    var str_uri = '/url';
    formData.append('id', int_id);
 } else {
    var str_action = 'create';
    var str_uri = '/url';
 }

 var xhr = new XMLHttpRequest();
 xhr.open('POST', str_uri, true);
 xhr.onload = function(e) {
    if (this.status == 200) {
      alert('success');
    }
 };
 xhr.send(formData);